Refers to the party that sends or consigns goods, typically in commercial shipping or freight contexts.
荷主は貨物の保険を手配した。
The shipper arranged insurance for the cargo.
運送会社は荷主から荷物を受け取った。
The transport company received the goods from the consignor.
Compound of 荷 (ni, 'cargo, freight') and 主 (nushi, 'owner, master'). The reading にぬし follows standard rendaku.